1. Field of the Invention
The present invention relates to a rotational connector device which is used in a relatively rotational component to perform an electrical connection for control of an air bag device incorporated in a steering device for an automobile or control of an audio device or a constant speed traveling device by a switch button provided on a steering wheel for an automobile.
2. Description of the Related Art
An example of this kind of rotational connector device includes a device where an annular space is formed between a rotor coupled to a rotating steering shaft and a stator coupled to a vehicle fixed side and a flat cable a winding direction of which is reversed in the middle is accommodated in the annular space in a winding state. One end of this flat cable is fixed to the rotor side, and the other end is fixed to the stator side. The flat cable is reeled out from a cylindrical wall surface of the rotor corresponding to a rotational direction of the rotor and is wound around a cylindrical wall surface of the stator or reeled out from the cylindrical wall surface of the stator and is wound around the cylindrical wall surface of the rotor. This movement is repeated, so that an angular change between the rotor and the stator due to a relative rotation therebetween is absorbed by a change of the winding state of the flat cable. A spacer is arranged between the rotor and the stator for regulating a route of the flat cable. Conventionally many rollers are supported on the spacer for reducing a sliding resistance to the flat cable, but in recent years, there has been made an attempt of reducing the number of the rollers in view of a reduction in costs.
For example, Japanese Patent Issue No. 4355229 discloses a rotational connector device in which a rotor is provided with an inner cylindrical portion and a stator is provided with an outer cylindrical portion wherein a spacer (holder) is rotatably arranged therebetween in a state of being supported by the stator. The spacer supports a single roller, and a plurality of guide portions are formed by intervals in the circumferential direction to sandwich the roller therebetween, each guide portion having a wall surface an outer envelope curve of which forms a circle and an inner envelope curve of which forms a circle concentric with the inner cylindrical portion. Each guide portion is formed in a frame shape having a closed plane configuration, and the outer surface forms a circular arc along the envelope curve. A circle formed by the outer envelope curve is eccentric to the inner cylindrical portion of the rotor, and intervals between the roller and each outer surface of the guide portions adjacent to both sides of the roller, and the outer cylindrical portion of the stator are made small, and on the other hand, an interval between an outer surface of the guide portion and the outer cylindrical portion of the stator present at an opposite side to the above guide portion in such a manner as to sandwich a rotational center of the spacer is made large. The flat cable wound around the inner cylindrical portion and the outer cylindrical portion is reversed between the roller and a side surface of the guide portion which is one of the guide portions adjacent to the roller. The flat cable rotates the spacer via a reverse section thereof corresponding to the rotational direction of the rotor.
However, the conventional rotational connector device is heavy since the spacer is structured such that many frame-shaped guide walls are provided to rise on the annular plate portion. As a result, because of a large sliding resistance to the flat cable generated at rotor rotating, there is a possibility that the flat cable buckles at the time the flat cable pushes a side wall of the guide wall.
In addition, in a steering wheel for an automobile, it is required to make rotation possible numbers (possible angles) in the right and left directions equal, and, for example for preventing the event that the flat cable can not rotate to a prescribed rotational number since the flat cable is tightly wound and fixed on the inner cylindrical portion in the middle of the rotating, it is absolutely required as a practical product to use a method that an indicator is incorporated in the spacer for indicating a neutral position to be used as an index on assembling. However, the rotational connector device disclosed in Japanese Patent Issue No. 4355229 can not set such an indicator. That is, according to the conventional rotational connector device, the circle formed by the envelope curve of the guide wall in the spacer is eccentric to the inner cylindrical portion and a large space is formed in a radial direction between the guide wall and the outer wall portion. Therefore the route of the flat cable, which will be reversed in the roller part and reeled out to the outer cylindrical portion side, varies. As a result, a reeling-out length of the flat cable is equal, but a rotational angle of the steering wheel is not constant, so that the indicator position can not be determined.